The 2-hour postprandial blood glucose (postprandial blood sugar, PPBS) test reflects the metabolic response to a carbohydrate challenge.⁹ In normal individuals, the blood sugar returns to the fasting level within 2 hours.

In contrast, postprandial hypoglycemia appears to result from delayed or exaggerated response to the insulin secreted in relation to dietary blood sugar rise. It may occur as an early event in individuals with non-insulin-dependent diabetes mellitus (NIDDM, type II diabetes mellitus) or in individuals with gastrointestinal malfunction. Frequently, no cause is demonstrated and the hypoglycemia is considered "functional." Postprandial hypoglycemia differs from fasting hypoglycemia (i.e., hypoglycemia that occurs after 10 or more hours without food) in that the latter nearly always has pathological significance. It results from either overproduction of insulin or undermobilization of glucose and is most commonly seen in clients with tumors of the pancreatic cells (insulinoma), liver disease, and chronic alcohol ingestion.¹⁰

With advancing age, the speed of glucose clearance declines. Two-hour levels in persons who do not have diabetes and in those with negative family histories may increase an average of 6 mg/dL for each decade over age 30 years.¹¹

[Show Table Outline]

Children

Adults

	Conventional Units	SI Units
Blood	120 mg/dL	6.6 mmol/L
Serum/plasma	140 mg/dL	7.7 mmol/L

Elderly Persons

	Conventional Units	SI Units
Blood	140 mg/dL	7.7 mmol/L
Serum/plasma	160 mg/dL	8.8 mmol/L

Note: Values may vary, depending on the laboratory method used.

[Table Outline]

• Children
• Adults
• Elderly Persons

• Failing to follow dietary instructions may alter test results.
• Smoking and drinking coffee during the 2-hour test period may lead to falsely elevated values.
• Strenuous exercising during the 2-hour test period may lead to falsely decreased values.

• Abnormal fasting blood sugar
• Routine screening for diabetes mellitus, as indicated by a blood glucose level greater than the fasting level and especially by a 2-hour level greater than 200 mg/mL
• Identification of postprandial hypoglycemia and differentiation of this state from fasting hypoglycemia, with fasting hypoglycemia almost always indicative of a pathological state
• Known or suspected disorder associated with abnormal glucose metabolism (see Table 5-2)
• Monitoring of metabolic response to drugs known to alter blood glucose levels (see Table 5-2)

Nursing Care Before the Procedure

General client preparation is the same as that for any test involving collection of a peripheral blood sample.

• Specific preparation includes ingesting a meal (usually breakfast) containing at least 100 g of carbohydrate 2 hours before the test.
• The American Diabetes Association recommends a 300-g carbohydrate diet for 2 to 3 days before the test, but this recommendation is not universally followed.
• The time of the last meal before the test should be noted.
• The client should then fast from food and avoid coffee, smoking, and strenuous exercise until the sample is obtained.
• Although medications are not withheld for this test, those taken should be noted.

Two hours after the carbohydrate challenge is ingested, a venipuncture is performed and the sample is collected in either a gray- or a red-topped tube, depending on the laboratory performing the test. A capillary sample may be obtained in children and in adults for whom venipuncture may not be feasible. Capillary samples are also used when the test is performed for mass screenings. Note that in some instances a fasting blood sugar level may be obtained before the carbohydrate challenge.

Nursing Care After the Procedure

Care and assessment after the procedure are the same as for any study involving collection of a peripheral blood sample. Resume usual diet and activities.

• Complications and precautions: Abnormal increased or decreased values are treated in the same way as for blood glucose testing. If the glucose level does not return to a fasting state in 2 hours, an additional glucose tolerance test is required, and there are no critical values to report.